1,720,985 research outputs found
A novel approach for longitudinal train dynamics simulations with multibody codes
No full textThe paper describes a novel approach to include longitudinal train dynamics within multibody codes by means of a dummy user force element. The latter solves the ordinary differential equations describing longitudinal train dynamics through the definition of additional dynamic states, and it calculates the in-train forces, which have a strong effect on the running safety of railway vehicles. The novel strategy allows to evaluate longitudinal train dynamics and multibody dynamics within the same computational framework, thus solving the dynamic states of both problems with the same numerical integrator. The method is first validated in simulation scenarios of an international benchmarking activity against traditional approaches and then it is applied to evaluate the dynamic safety of an emergency braking operation of a European freight train. With respect to developing multibody models with one body per vehicle in the train consist, the novel approach can be up to four times faster. Moreover, the novel method proves to be faster by up to one order of magnitude when compared to co-simulation strategies, whose accuracy is strongly related to a proper tuning of the communication rate
A new finite element axisymmetric model with non-axisymmetric thermal loads for thermal analyses of tread braked wheels
Full text linkThe paper describes the implementation of a finite element (FE) model for the calculation of the temperature field on tread braked wheels in ANSYS Mechanical APDL. The model is based on axisymmetric-harmonic elements, that allow to apply non-axisymmetric thermal loads over an axisymmetric geometry, thanks to the definition of thermal loads in terms of Fourier series coefficients. The model is benchmarked against a reference 3D model, in steady-state and transient simulations, and it provides the same outputs with improved computational times and management of memory resources. As the new model has 390 fewer degrees of freedom with respect to the 3D model, speed up factors around 1580 can be achieved, and smaller step-sizes are enabled
Application of low-power energy harvesting solutions in the railway field: a review
No full textIn order to ensure safety and reliability of railway transportation the interest in monitoring systems is constantly increasing. These devices include sensors and electronic components, which need electric power supply for their proper working. However not all railway lines and vehicles are provided with electric power, furthermore, it can be complex to provide energy to sensors by cables in some location of the vehicle. The demand of a widespread distributed electrical energy can be fulfilled by energy harvesting techniques from primary sources. This paper analyses the different concepts of energy harvesters proposed in literature for the railway field, both for on board and wayside applications. The harvesters are classified according to the source from which energy is harvested and for each type of harvester advantages and disadvantages are critically discussed. The proposed review highlights the most promising solutions regarding energy harvesting in order to support future researches concerning this topic
Design of an Innovative Twin-Disc Device for the Evaluation of Wheel and Rail Profile Wear
Full text linkThe tribological properties of steels used to realise railway wheels play a fundamental role in the performances of both vehicle and infrastructure. In particular, the wear process, caused by the wheel–rail interaction, modifies the shape of wheel and rail profiles, changing the performances of the vehicle. For this reason, research institutes and vehicle manufacturers have worked hard to develop predictive tools able to estimate the evolution of the wheel and rail profiles. The efficiency of these tools is strongly influenced by the tribological properties of the materials, i.e., the wear coefficients, which are used as input data. The characterisation of these properties requires specific tools and long-lasting experimental campaigns, which are usually performed under controlled operating conditions, using twin-disc test benches. These devices usually do not consider the real contact conditions in terms of normal load, contact geometry, and slip velocity, since they are equipped with small-size rollers. The paper proposes an innovative 1:5 scaled twin-disc, which allows the reproduction of the real wheel–rail contact conditions, thanks to Pascal’s scaling technique. The testing device allows the reproduction of a wide range of typical operating conditions of railway vehicles, thanks to high-power independent brushless motors, used to actuate the rollers, and an innovative loading system
Adapting a scaled twin-disc device for tread braking investigations based on an ad-hoc thermal similitude model
Full text linkThe present paper shows the design of a scaled tread braking system to be included in a scaled twin-disc system, to carry out thermomechanical investigations on wheel and shoe materials. The test bench consists of two discs, pressed against each other, simulating the wheel-rail contact. A pneumatic cylinder pushes scaled brake shoes against the wheel tread surface, and a fan-nozzle device improves convection cooling. As a major novelty, both systems are designed to comply with a new thermal scaling method, that is specifically identified to obtain the same temperature field on the scaled twin-disc as for a full-scale system. The paper thoroughly describes the mathematical background of the new thermal scaling method, which is then preliminarily validated with finite element thermal models for both the brake block and wheel. The greatest advantage of the final twin-disc configuration is that it allows to carry out investigations of wheel-rail wear phenomena as well as studies on the thermomechanical interaction between wheels and brake shoes, while adhering to scaling rules that corroborate the validity of the experimental results
Validation of a brake monitoring system using a multi-axle roller-rig
No full textA widespread diffusion of monitoring systems is the key to improving safety and reliability of railway vehicles and to reducing maintenance costs by increasing the lifetime of structural and mechanical components. Several on-board devices have been conceived in recent years to detect faults on critical parts, by monitoring the real-time conditions of wheelsets, bearings, brakes, bogie, carbody, etc. These systems rely on powered sensor nodes, mounted on different parts of the vehicle, which acquire signals of interest and use proper algorithms to detect component faults or train derailments. Roller-rigs represent a good solution to develop and validate new monitoring devices with good repeatability of test conditions. The research group from Politecnico di Torino realized an innovative 1:5 scaled roller-rig, consisting of four wheelsets running on the same pair of rollers, originally used for investigations on wheel-rail adhesion. Then, minor changes were made to simulate and test a braking system monitoring device. Each wheelset is provided with a braking system, consisting of two brake discs and two brake callipers, while the rollers are powered using one AC brushless motor. A freight train pneumatic system is reproduced thanks to three electropneumatic regulators, which simulate the pressure in brake pipe, auxiliary reservoir and brake cylinder. The test bench and the motor drive are managed by an industrial PC using the software LabVIEW, allowing to perform braking operations of a real vehicle. Sensors are installed to measure wheelset speed, calliper temperature and pressures in the braking system. These signals are sent to an electronic control unit, which could be provided with a fault detection logic. The paper deals with the experimental setup of the bench and the preliminary results obtained by laboratory tests, which highlighted that the apparatus can be a reliable tool to develop new monitoring algorithms for train braking systems
The Effect of the Calculation of Slip Speed on the Wear of Wheel Profiles: A Benchmarking Against the SIMPACK Wheel Profile Wear Module
No full textThe efficiency of modern computers in the solution of railway vehicle dynamics with multibody codes is currently leading the path towards the development of numerical tools for the evaluation of wear of the wheel profiles starting from the outputs of dynamic simulations. The latter are commonly launched in commercial software packages, which guarantee unbeaten reliability and stability of their numerical solvers, as well as simple user-friendly interfaces. Many commercial multibody codes are currently provided with add-ons for the evaluation of wear of wheel profiles, however the limited number of tuneable parameters can compromise the stability of the simulation. The present paper aims to benchmark the outputs of the SIMPACK Wheel Profile Wear module and to investigate the differences due to the application of the Archard’s law in local form, focusing on different strategies that can be adopted to calculate the slip speed on the contact patch with the FASTSIM algorithm. It is found that recent expressions suggested in the literature for the calculation of the equivalent flexibility should be preferred over the original equation when calculating the slip speed in each cell of the contact patch grid
Integration of brake block thermal equations within a railway vehicle multibody model: a multiphysics approach
No full textThe paper shows the development of a finite-difference (FD) railway brake block thermal model and its integration within the multibody (MB) formalism of the Simpack commercial code. The block nodal temperatures are included among the dynamic states computed by the MB solver, through the definition of a user-defined force element, which determines the braking torque based on the applied brake cylinder pressure. The proposed approach overcomes the main limitations of existing detailed railway vehicle models, which solve the thermal and vehicle dynamics equations in different computational environments. Furthermore, the new strategy can thrust the development of models able to account for the coupling between the wheel and block thermal behaviour and the whole vehicle dynamics. Preliminary simulations of drag and stop braking operations of a reference European freight waggon prove that the proposed model is able to effectively consider the main heat fluxes and nonlinearities involved in tread braking operations
Calculation of Wear of Railway Wheels with Multibody Codes: Benchmarking of the Modelling Choices
Full text linkThe numerical simulation of wear of railway wheel profiles can be a game changer in the railway field, as it can drive the planning of wheel re-turning operations, thrust the identification of optimized profiles and evaluate the safety of railway vehicles at the early stages of design. Today, commercial multibody codes are provided with dedicated routines that can evaluate the worn profile shape due to the dynamic behaviour of the vehicle. As the outputs of such modules can depend on different user-selectable parameters and modelling choices, it is vital to assess the capabilities of these codes and get a further understanding of the implemented algorithms. This paper aims to benchmark the effects of different modelling parameters and choices, mainly related to the selected wear law and wheel–rail contact method, on the final wear outputs, with special reference to the wear module provided by the SIMPACK commercial multibody code. A relevant novelty of the paper deals with the benchmarking of the wear algorithm available in the commercial code with in-house wear routines, comparing different strategies and choices for the calculation of wear. This allows us to better understand the most critical differences and modelling issues, as well as to highlight possible improvements in wear algorithms that can lead to enhanced numerical stability. More in detail, this work suggests a change in the wear algorithm that proves to be beneficial to removing local wear peaks produced by numerical sources, which could cause instabilities in the computation
Long train dynamic simulation by means of a new in-house code
No full textThe need for faster heavy-haul trains with higher axle-loads is responsible for the rise of large in-train forces on wagon connection systems. These forces have a significant impact on longitudinal train dynamics (LTD) from the point of view of performances, running stability and safety during braking and traction operations. Therefore, LTD simulations represent an essential tool to predict in-train forces and to design coupling and braking systems. Long trains are typically modelled as a system of several point masses linked to each other by means of non-linear elements, summarizing the characteristics of the coupling systems. In fact, wagon connection systems present a non-linear force-deflection characteristic, with a hysteresis loop due to the different behaviour in loading and unloading states. The calculation of in train forces is nowadays performed following three main strategies, namely look-up table approaches, mathematical equations based on experimental results and “white-box” models related to physical properties of the connection systems. An International benchmark of LTD simulators was recently proposed to assess the output results obtained by different simulators, following several modelling strategies, in the simulation of the same scenarios. The research group from Politecnico di Torino joined the competition using the multibody commercial software Simpack (ver.9.4). However, inefficiencies appeared because multibody software are usually intended for the simulation of a few vehicles with many degrees of freedom (d.o.fs), rather than many wagons with few d.o.fs each. Therefore, the team developed a new LTD simulator (LTDPoliTO) in MATLAB, totally based on a vector-arithmetic logic. The new simulator can perform both dynamic investigations in time domain and modal analysis in frequency domain. The validation of LTDPoliTO was carried out by performing the four benchmark simulations and a good agreement with the other participants was obtained, in terms of both numerical results and computational speeds
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